Thales Alenia Space’s Stratobus flies at 20 kilometers in altitude and triples the amount of solar illumination on its solar panel through the use of solar concentrators lining the floor of the 100-meter-long platform. The solar array, shown at the top of the otherwise transparent roof, collects power from the concentrators below and from the sun directly to produce 150 kilowatts per day to power both the vehicle and a payload of up to 250 kilograms. Credit: Thales Alenia Space

The Stratobus backers are focusing only on Earth observations in the tropical regions for the moment, but expect to add telecommunications payloads once international regulators have authorized HAPS systems to operate in Ka- and Ku-band.

The U.S. government is leading the effort at the ITU to broaden the frequency regime for HAPS and high-altitude drones to Ka- and Ku-band, already in mainstream use by satellite fleet operators.

The U.S. position met with substantial resistance – for reasons that were never made clear — at the last quadrennial meeting of global regulators, WRC-15, which agreed only to create a study group to examine the issue in view to a decision at WRC-19.

Until then, Thales Alenia Space’s Stratobus will limit itself to optical and radar Earth observation, said Jean-Philippe Chessel, head of the Stratobus project.

“If [the ITU decision at WRC-19] is positive, it will clearly open the telecommunications market for HAPS and for Stratobus,” Chessel said June 30 at the Toulouse Space Show.

The French-Italian Thales Alenia Space announced Stratobus in April following the receipt of 17 million euros ($19.2 million) in financing from France’s PIA Investing in the Future public bond fund, plus 3 million euros from four regional governments in France that are home to the Stratobus industrial team.

Chessel said the industrial partners are financing 60 percent of the development over the next two years, with French government support totaling 40 percent.

The commercial version of Stratobus will measure 100 meters in length, as long as an Airbus A380, and 33 meters in diameter at its widest point. Its four electric-powered engines are designed to keep the platform steady at 20 kilometers in altitude in headwinds of up to 90 kilometers per hour. Air density at that altitude is less than half what it is on the ground.

It will carry a payload, typically a radar or optical Earth observation sensor, weighing up to 250 kilograms, that will image an areas of between 250 and 300 kilometers for radar applications, and 40-60 kilometers for optical.

The top half of Stratobus is transparent material. Attached to the underside of its roof is a solar panel drawing power both from the Sun above, and below from a row of solar power concentrator mirrors lining the floor.

The space industry last viewed solar concentrators on the first models of Boeing’s large 702 telecommunications satellite platform. A design flaw caused the concentrators to damage the solar panels and resulted in reduced power, causing large insurance claims for the first batch of satellites. Boeing subsequently dropped the concentrator design, although in the years since then the damage to the satellites in terms of reduced operational life turned out to be less than originally feared.

Chessel said the concentrators will triple the amount of solar illumination onto the solar array and provide the 150 kilowatts power day of total power demand for Stratobus, of which 5 kilowatts will be reserved for the payload.

Stratobus’s volume is 50,000 cubic meters. Chessel said the pressurized gas will be either helium or hydrogen, with hydrogen preferred because it is less costly to produce and is lighter, saving 300 kilograms over helium. But hydrogen has the downside of requiring special safety procedures.

Operating in the tropics with sufficient sunlight year-round, Stratobus could remain on station for up to five years, Chessel said. At more-northern latitudes, the platform would be limited to the spring and summer months and could operate for eight months.

Chessel said the current budget is enough to carry the project’s development for two years. A critical design review is planned for 2018, after which a full-size test model could be flown in 2020. Thales Alenia Space has begun the process of Stratobus flight certification with the European Aviation Safety Agency. A new certification category is needed because HAPS platforms like Stratobus fall somewhere in between the existing regulations for balloons and drones.

“We expect to have our first contract in 2017 to develop the first proto-flight model,” Chessel said. “It will be paid by the first customer and lead to the production of future flight models. Stratobus is a low-cost product, an order of magnitude less costly than a satellite, plus the fact that we don’t have a launcher. We can take off and land by gas management and we don’t need space-qualified components. Of course, this is a regional product only. It doesn’t provide global coverage like a satellite. The prospects we have today suggest we are going in the right direction in terms of product.”

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